Compaction waves in granular HMX

Menikoff, Ralph; Kober, Edward
April 2000
AIP Conference Proceedings;2000, Vol. 505 Issue 1, p397
Academic Journal
Piston driven compaction waves in a granular bed are simulated with a two-dimensional continuum mechanics code in which individual grains are resolved. The constitutive properties of the grains are modeled with a hydrostatic pressure and a simple elastic-plastic model for the shear stress. Parameters are chosen to correspond to inert HMX, and the initial bed chosen to represent a tightly packed random grain distribution with 19% porosity. By varying the piston velocity, waves were obtained ranging from weak partly compacted waves to strong fully compacted waves. The average stress and wave speed are compatible with the porous Hugoniot locus for uniaxial strain. However, the heterogeneities give rise to stress concentrations which lead to localized plastic flow. For weak waves, plastic deformation is the dominant dissipative mechanism and leads to dispersed waves that spread out in time. In addition to dispersion, the granular heterogeneities give rise to subgrain spatial variation in the thermodynamic variables. The peaks in the temperature fluctuations, known as hot-spots, are in the range that would have a critical effect on ignition sensitivity.


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